In manufacturing semiconductor devices, microfabrication is generally carried out according to lithography techniques by use of photoresist. The process of microfabrication comprises the steps of: forming a thin photoresist layer on a semiconductor substrate such as a silicon wafer, exposing the layer to active rays such as UV light through a mask pattern corresponding to the aimed device pattern, developing the exposed layer to obtain a photoresist pattern, and then etching the substrate by use of the obtained photoresist pattern as a protective film so as to form a fine relief or intaglio pattern corresponding to the above pattern on the substrate surface. In this technological field, integration degree of the devices has been increased lately and accordingly there has been a tendency of adopting very short-wavelength light, such as, KrF excimer laser (wavelength: 248 nm), ArF excimer laser (wavelength: 193 nm), extreme ultraviolet light (EUV, wavelength: 13.5 nm) or electron beams (EB), as the active rays in the exposure step. However, in the photolithographic process, the substrate may reflect light to generate standing waves and/or the exposure light may be reflected diffusely by bumps of the substrate. Consequently, the process often suffers from a problem in that dimension accuracy of the pattern is lowered. Further, when very short-wavelength light such as EUV is employed as the exposure light, the resist layer may be adversely affected by gases given off from the substrate placed thereunder. In order to solve this problem, it is widely studied to form a bottom anti-reflective coating between the substrate and the photoresist. The bottom anti-reflective coating is required to have various properties. For example, it is preferred for the bottom anti-reflective coating to largely absorb radiation used for exposure of the photoresist, to prevent diffused reflection and the like so that the exposed and developed photoresist can have a cross section perpendicular to the substrate surface, and to be insoluble in solvents contained in the photoresist composition (namely, not to cause intermixing). The intermixing is particularly serious because it often gives adverse effects to the interface between the photoresist layer and the bottom anti-reflective coating. Accordingly, the intermixing may make it difficult to control the pattern or shape of the photoresist.
Lithography techniques with electron beams or EUV (wavelength: 13.5 nm) have been receiving a lot of attention for these years. However, even if the lithography techniques with electron beams or EUV is adopted in a device-manufacturing process, a resist pattern having an undercut or skirt shape is formed but it is impossible to form a resist pattern having a favorable rectangular shape. That is because the electron beams, EUV or the underlying substrate adversely affects formation of the resist pattern. The unfavorable pattern shape is liable to cause various problems, such as, increases of pattern sidewall roughness (line edge roughness, LER) and line width roughness (LWR), such insufficient adhesion between the resist pattern and the substrate as to cause pattern collapse, shallow depth of focus, low sensitivity, and low etching rate. Accordingly, in the electron beam- or EUV-lithographic process, it is necessary to replace a conventional anti-reflective resist underlayer film (i.e., anti-reflective coating) with an electron beam or EUV lithography-oriented resist underlayer film capable of reducing adverse effects of the electron beams or EUV and thereby of making it possible to form a favorable resist pattern.
In Non-patent document 1, polymers having low thermal expansion coefficients are employed to improve pattern collapse and LWR. Also as described in Patent documents 1 to 3, conventional electron beam or EUV lithography-oriented resist underlayer films are mainly made of polymers. Those polymers used in prior arts have large molecular weight distributions, and hence the formed underlayer films are thought to be largely inhomogeneous in inner density. Accordingly, since it is difficult to form a uniform film serving as the underlayer film, the formed film often suffers from collapse of resist pattern and is not homogeneously affected by adverse effects of the electron beams, EUV and/or the underlying substrate. Thus, it cannot be said that those prior arts fully improve LWR.    [Patent document 1] Japanese Translation of PCT International Application Publication No. 2008-501985    [Patent document 2] International Patent Publication No. 2011/074494    [Patent document 3] International Patent Publication No. 2012/017790    [Non-patent document 1] Proc. SPIE, Vol. 7972, 797211(2011)